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gregsenne 10-10-2012 09:18 AM

Vapor barrier on basement wall
My basement is heated/cooled. The walls are cinder block, and the basement has the perimeter drain all the way around it. It used to have problems with leaking, until we dug out the outside, waterproofed everything, added a sump pit, and lots of drainage tile. No problems yet, but I want to plan for a problem should it happen after I finish the basement.

Currently, the unfinished basement just has about 4 ft tall blanket insulation around all walls, hung from the ceiling. So from the floor to 5 ft up, there is no insulation. The blanket insulation has the fiberglass up against the cinder block, and a white vapor barrier towards the basement. I guess this is fine because the lower part of the basement is below the frost line.

I want to add poly sheeting to the wall and tuck it into the perimeter drain, should any water get through, it will roll down into the drain. So, should I just connect the poly sheeting to the bottom of the vapor barrier on the blanket insulation, and run it down to the ground?
Should I poly sheet the whole wall, then put the blanket insulation on top of that?
For cost saving, I would rather keep the blanket instead of buying batts for the walls, if at all possible.
Is it okay for fiberglass insulation to be directly on the cinder block? What if water leaks and gets on the fiberglass? Would I have to worry about mold?

Ive also heard that I cant have the vapor barrier on there because the outside of the cinder block wall is waterproofed? On the outside, we had this company come in and spray this really thick chunky black tar stuff on the outside of the cinder block wall.

BTW, house is in southern Ohio.

Whats the best way to do this?

Windows on Wash 10-10-2012 07:39 PM

You have an internal drain tile or exterior?

gregsenne 10-10-2012 09:16 PM

Both. There is tile outside and completely under the basement floor that all go to a sump pit. The perimeter drain drains to the gravel under the floor, which should filter into the tile.

AllanJ 10-11-2012 07:31 AM

No vapor barrier on the inside because you already have a vapor barrier (black goop) on the outside of the concrete foundation.

If you use paper (or plastic) faced batts, cut out slots or squares in the paper surface after stapling the batts in place. Remove at least 25 percent of the total paper area but not in a manner that would cause the batts to sag.

There should be a one inch gap between batt insulation and the concrete wall. If you are concerned about water seepage you might want to honor that gap even if you use foam insulation. Then any water that comes in above floor level will run down to the floor and drain into the gap between floor and wall and then into the gravel below.

Less than perfect backfilling outside can leave air pockets that collect water where some water may seep through imperfections in the black goop and through the concrete foundation before it all can soak down into the ground outside.

Gary in WA 10-12-2012 11:27 PM

Fiberglass batt and a vapor barrier poly would be Case #3, pp.8: Follow through reading about that wall starting page 26 to the end...

The foam board needs to be thick enough to use a vapor retarder (if needed at all). The wall needs to be fire-stopped every 10' horizontally, per code; You don't want an outlet fire to run the wall length unhampered to enter a joist space above and go to the attic through a wiring/plumbing hole at an interior wall. Removing 25% paper facing leaves 75% effective vapor retarder (not an air barrier) left;

With the interior drain, I'd use some foam board on the poly sheeting against concrete, being sure it is air-tight= compare those other wall designs in the first link. Then a vapor barrier on each side of the concrete would be acceptable if the wall can dry to the outside above grade, Post # 25;

No gaps to the insulation for convective loops;


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